Embodiments of the present invention relate generally to a pharmaceutical syringe piston, and more particularly, to a pharmaceutical syringe piston with an improved inert film attachment.
U.S. Pat. No. 7,547,297 discloses a rubber syringe piston partially enclosed by an inert film in a cap-like manner. Specifically, the inert film is placed on an outer surface of a tapered face of the piston which faces the contents of a syringe. The inert film prevents contamination of the medicament by materials leaching out of the stopper, and similarly prevents the medicament from penetrating the stopper during extended storage periods, preserving the longevity of the stopper.
However, the film in U.S. Pat. No. 7,547,297 also extends along a cylindrically-shaped portion of the piston. Applicant has discovered that, as a result of this configuration, the inert film abuts against an interior wall of the syringe barrel. This arrangement can increase the breakloose and extrusion (BLE) forces between the stopper and syringe barrel. Higher BLE forces can result in slippage or other errors during injection as the user applies greater pressure to the stopper in order to expel the medicament. In addition, the film contact with the syringe barrel reduces the ability of the rubber material of the stopper to create a seal. The desired seal is at its highest quality when the rubber directly contacts the inner surface of the syringe barrel.
It is desirable to provide a syringe piston that produces low BLE forces with the inner surface of the syringe, and which creates an acceptable seal with the inner surface of the syringe, while still utilizing an inert film to prevent cross-contamination of the syringe piston material with the medicament.